1. Field of the Invention
The present invention relates to a switching regulator that is disposed as a power source of a portable apparatus or an electronic apparatus so as to output a constant voltage, and more particularly, to an overshooting suppressing circuit that can suppress overshooting in an output voltage.
2. Background Art
FIG. 5 is a circuit diagram illustrating a switching regulator according to the related art.
The switching regulator according to the related art includes a power source terminal 101, a ground terminal 102, a reference voltage circuit 111 that outputs a reference voltage, a voltage divider circuit 112 that divides an output voltage VOUT of an output terminal 103, an error amplifier 110 that outputs a voltage VERR which is a comparison result of the divided voltage with the reference voltage, a ramp wave generator circuit 114 that generates a ramp wave VRAMP, a PWM comparator 113 that compares the voltage VERR with the ramp wave VRAMP and outputs a signal PWM, an output buffer 115, an output transistor 116, and a soft start circuit 117.
The operation of the switching regulator according to the related art will be described below.
When a voltage VDD is applied to the power source terminal 101, the error amplifier 110 compares the reference voltage VREF output from the reference voltage circuit 111 with the divided voltage VFB obtained by causing the voltage divider circuit 112 to divide the output voltage VOUT and outputs the voltage VERR. The PWM comparator 113 compares the voltage VERR with the ramp wave VRAMP and outputs the signal PWM to the output buffer 115. The output buffer 115 outputs the signal PWM to the output transistor 116 under the control of the output signal of the soft start circuit 117. The soft start circuit 117 has a function of slowly increasing the output thereof when the voltage VDD is applied to the power source terminal 101. Accordingly, by causing the output buffer 115 to slowly turn on the output transistor 116, the overshooting in the output voltage VOUT of the switching regulator is suppressed.
[Patent Document 1] Japanese Patent Application Laid-Open No. 2008-11585